hot spot

1. (primarily used by C/Unix programmers, but spreading)
It is received wisdom that in most programs, less than 10% of
the code eats 90% of the execution time; if one were to graph
instruction visits versus code addresses, one would typically
see a few huge spikes amidst a lot of low-level noise. Such
spikes are called "hot spots" and are good candidates for
heavy optimisation or hand-hacking. The term is especially
used of tight loops and recursions in the code's central
algorithm, as opposed to (say) initial set-up costs or large
but infrequent I/O operations.

2. The active location of a cursor on a bit-map display. "Put
the mouse's hot spot on the "ON" widget and click the left
button."

3. A screen region that is sensitive to mouse clicks, which
trigger some action. Hypertext help screens are an example,
in which a hot spot exists in the vicinity of any word for
which additional material is available.

4. In a massively parallel computer with shared memory,
the one location that all 10,000 processors are trying to read
or write at once (perhaps because they are all doing a
busy-wait on the same lock).

5. More generally, any place in a hardware design that turns
into a performance bottleneck due to resource contention.